This invention relates to composite bearings, and, more particularly, to an improved composite ball and socket bearing.
Spherical journal bearings are designed for applications where both misaligning and oscillatory motions are present. These bearings are also referred to as self-aligning bearings, typically comprising a bearing with a spherical outer diameter, referred to as the ball, mounted within an opening or the socket of a housing, to form the ball and socket bearing. The socket comprises a concave inner surface or raceway that is integral with the housing. In such ball and socket bearings the socket housing is frequently termed a pillow block. The socket inner raceway and the outer spherical diameter of the ball must have a very closely toleranced fit to assure consistent bearing performance and long life.
The ball is often designed to be removable from the socket to allow the ball to be replaced as it wears or as the requirements for the bearing change. Such a removable ball and socket bearing is shown in U.S. Pat. No. 3,116,539, issued to Evans et al. on Feb. 21, 1961, which discloses a socket having slots diametrically spaced apart on one side of the inner diameter of the socket, permitting insertion of the ball into the socket inner raceway. The ball is inserted sideways into the insertion slots and turned ninety degrees to seat the spherical outer diameter of the ball within the socket inner raceway, making the ball easily removable from the socket. The socket may then be permanently mounted and the ball replaced as necessary. The insertion slots reduce the surface area of the concave inner raceway, and must be carefully formed to avoid producing irregularities in the inner raceway surface which might lead to increased wear.
An alternative means for replaceably mounting a ball within a permanently mounted socket is disclosed in U.S. Pat. No. 3,998,504, issued to McCloskey on Dec. 21, 1976. This patent discloses a ball and socket type bearing wherein the inner raceway of the socket member is on a separate three unit intermediate socket member assembled or built up within a bore in the rigid housing member, or pillow block. The intermediate socket is assembled from two partial annular subunits which removably line part of the bore of the pillow block, leaving a small annular gap, or slot for insertion of the ball. The partial subunits have a concave inner surface or raceway for seating the ball in the completed assembly. After the ball has been placed within the partial annular raceway defined by the two partial annular subunits a third subunit, or key, is inserted into the annular gap to complete the intermediate socket and the ball is turned to seat the spherical outer surface thereof within the newly completed three piece raceway.
A problem with this bearing arrangement is that an installation clearance must exist between the interfaces created between the three socket subunits. Because of such clearances the interfacing edges of the subunits cannot be perfectly aligned annularly along the inner raceway, and the play existing between the interfacing edges make it impossible to produce a tightly toleranced fit between the inner raceway of the assembled intermediate socket and the spherical outer diameter of the ball inserted therein. These interfaces break up the smooth surface of the inner race and lead to increased wear of the bearing surface.
One solution to the problem of maintaining a close toleranced fit between the ball outer surface and the socket inner raceway is to permanently mount the spherical ball in the inner raceway of the socket member, to produce a unitary ball and socket bearing. Many such bearings are known having metallic socket members permanently forged or otherwise formed onto metallic balls. Such unitary ball and socket bearings are difficult and expensive to manufacture, and there is always a risk of the final assembly causing damage to either the ball outer surface or the socket inner raceway which would adversely affect the close tolerance bearing interface. Further with this design the ball is not replaceable and therefor the housing containing the socket cannot be permanently mounted.
Another type of composite ball and socket bearing is disclosed in U.S. Pat. Nos. 3,700,295 and 3,974,009, both issued to Butzow et al., on Oct. 24, 1972 and Aug. 10, 1976, respectively. This bearing comprises a resin-impregnated filament-wound annular intermediate socket member having a concave inner raceway and a corrosion resistant spherical steel ball, which overall produces a lightweight, corrosion-resistant composite ball and socket bearing. This combination of a ball and an intermediate socket member will be referred to as a bearing subassembly because it is designed to be replaceably mounted within a permanently mounted socket housing or pillow block. The bearing subassembly also has a self-lubricating surface of a low friction material, such as a woven Teflon fabric, on the inner raceway of the annular intermediate socket member, which is produced by a method comprising applying the fabric over the spherical steel bearing assembled on a mandrel and then building up the body of the annular intermediate socket member over the fabric by repeatedly winding resin-impregnated fiberglass filaments about the fabric. The resulting resinous body is subsequently cured to harden the resin. The inner raceway surface thus comprises a layer of Teflon fabric, which forms a low friction bearing surface against the outer surface of the steel ball. This type of bearing subassembly also provides the desired tightly toleranced fit between the outer spherical diameter of the ball and the intermediate socket inner raceway. With a fiberglass intermediate socket member formed over a steel ball in this fashion, a replaceable bearing subassembly is produced which is lighter, less expensive and easier to manufacture than a bearing subassembly having a metallic socket member formed over a metallic ball.
The intermediate socket member must be mounted and then retained within the socket of the pillow block housing without affecting the freedom of the ball to rotate within the intermediate socket member. The socket of these composite bearing subassemblies typically comprises a cylindrical bore in the pillow block housing. The intermediate socket member is provided with a cylindrical outer diameter dimensioned to fit within the cylindrical bore of the pillow block, with the pillow block bore functioning as a socket for the bearing subassembly. This provides a three piece bearing assembly comprising the pillow block, the intermediate annular socket member and the spherical ball.
Because such a bearing subassembly will be exposed to both misalignment and radial loads, the mounting of the bearing subassembly frequently fails before the bearing subassembly wears out and such mounting failure may also damage the pillow block housing necessitated by its replacement. Mounting of the bearing subassembly by press fitting, bonding or by retaining means such as snap rings, machined shoulders or swaged collars have all been utilized to retain the bearing subassembly in the pillow block socket.
Problems exist for these solutions, however. Bonding of the intermediate socket member within the pillow block bore is permanent, because it makes replacing of the bearing subassembly all but impossible, and is not preferred for this reason. The retaining means are undesirable because they create stress points which frequently translate into early failure of the fiberglass intermediate socket member, particularly in applications with high force dynamic axial loads, due to galling, chipping or fracturing. In such applications bearing subassemblies having a fiberglass annular intermediate socket member tend to be less durable than similar ball and socket composites having both metallic balls and metallic intermediate socket members, but high axial or radial loads may cause high wear rates or even failure in the mounting region of metallic components. Therefore an improved ball and socket bearing is needed which will have a bearing subassembly that will have a one piece intermediate socket member replaceably mounted on the pillow block in a manner that will not lead to unacceptably high wear or premature failure of either the intermediate socket member or the pillow block in which it is mounted. The replaceable mounting must allow the bearing subassembly to be easily removed and replaced while securing the bearing subassembly to send radial and axial loads.